HTT and Huntington disease: The resulting expression of the mutant huntingtin protein (mHtt) elicits a loss of gamma-aminobutyric acid (GABA)ergic striatal projection medium spiny neurons (Vonsattel and DiFiglia, 1998) leading to a striatal atrophy, which is correlated with clinical motor impairment, the most characteristic symptom in HD (Guo et al., 2012).